Things get fixed during the day. I can't remember anything failing between soundcheck and show. Remember, everything is incredibly well maintained and checked daily. There are boffin gear techs and electricians on the tour. So if an amp needs fixing or a pedal, it will be looked at during the day before soundcheck.
A lot of times you are in cities where replacement parts or gear can be sourced. There were two tofu week gaps between legs of the tour, so replacements can be shipped in during those time periods.
I don't remember anything failing, certainly not in the drums and percussion. Drumheads and guitar strings are changed, renewed, while they are still in good condition, just in case.